The present invention relates to an ink jet printing apparatus which operates on a novel and heretofore unexploited principle.
Two types of ink jet printing apparatus are well known in the art. In the first type, a steady jet of electrostatically charged ink particles is ejected from a nozzle. Where it is desired to print a dot, an electric deflecting potential is applied to an electrode causing the jet to deflect above a gutter and impinge against a sheet of paper. In the second type, a group of ink particles is ejected from a nozzle in response to an ultrasonic signal applied to a piezoelectric element or bundle of thin wires provided in the nozzle and impinges on a sheet of paper. The first type ejects ink continuously whereas the second type ejects ink on demand.
There is increasing demand in the art for very high resolution printing. Whereas the diameter of dots in conventional ink jet printing is on the order of 100 microns, a dot diameter of 50 microns or less is required for high resolution printing. The diameter of the nozzle orifice must be extremely small and precise, making it very difficult and expensive to machine such nozzles. In addition, such a small diameter orifice tends to become clogged with ink very easily.
Other problems are encountered where a plurality of nozzles are provided in a multi-head arrangement comprising a separate drive control system for each nozzle. The kinetic energy of the ink in the nozzles varies due to differences in the diameters and lengths of the nozzles, pressure pulsations in the ink supplied to the nozzles from a low pressure pump, variations in the electrical parameters of the piezoelectric drive elements, etc. Another problem involves electric fields and air currents between the nozzle and paper which deflect the ink drops from the proper printing positions in a random manner.